Besides the documentation, that is, this book, there are other
resources about PostgreSQL:

Wiki

The PostgreSQLwiki
contains the project's FAQ (Frequently Asked Questions) list,
TODO list, and detailed information about many
more topics.

Web Site

The PostgreSQLweb site
carries details on the latest release and other information
to make your work or play with PostgreSQL more productive.

Mailing Lists

The mailing lists are a good place to have your
questions answered, to share experiences with other users,
and to contact the developers. Consult the PostgreSQL web site for details.

Yourself!

PostgreSQL is an
open-source project. As such, it depends on the user
community for ongoing support. As you begin to use
PostgreSQL, you will rely
on others for help, either through the documentation or
through the mailing lists. Consider contributing your
knowledge back. Read the mailing lists and answer
questions. If you learn something which is not in the
documentation, write it up and contribute it. If you add
features to the code, contribute them.